Electronically scanned antenna system



June 26, 1962 F. E. GOODWIN ETAL ELEcTRoNIcALLY scANNED ANTENNA SYSTEM 4 Sheets-Sheet 1 Filed Nov. 28, 1958 .NNN

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ELECTRONICALLY SCANNED ANTENNA SYSTEM Filed Nov. 28. 1958 4 sheets-sheet 2 June 26, 1962 3,041,605

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' I'OWS United StatesPatent dC) 3,041,605 p ELECTRQNICALLY SCANNED ANTENNA SYSTEM Francis E. Goodwin, Los Angeies, and John Sur, Manhattaneach, Calif., assignors to Hughes Aircraft Company, Culver City, Calif.,'a corporation lof Delaware Filed Nov. 28, 1953, Ser. No. 777,550 "7 Claims. '(Cl. 343-100) `The "presentiinvention relates to an electronically `scanned vlantenna Vsystem and more particularly to an antenna system having a .plurality ofreciprocal phase shifters programmed to provide a raster ltype volumetric scan from a fixed type antenna.

VThe disadvantages of mechanical types of scannmg are wellv known in the art Iand to overcome such disadvantages av number of antenna system have been developed employing a variation of the frequency of mlcrowave .energy utilized to excite the antenna. Most of such systems provide electrical scanning of space 1n one d1- mension, but still require mechanical movement of the antena toinclude a second dimension.

With the recent advancement in the development of *microwave components having elements of a ferromagneticdielectric material, it becomes possible to have an electronically scanned antenna system for two-dimensional scanning of space; however, such phase shifters as developed todate have not met the exacting characteristics or requirements necessary for such a system. The referenced characteristics include phase shift reciprocity, accurate high speed switching, economy of driving power,

Patented June 26, 1962 rice lar lwaveguide with a portion of the broad wall dimension reduced. A solenoid is wound about the waveguide at the reduced dimension to produce a longitudinal magnetic eld through an element of ferrite material mounted centrally within the waveguide between the broad walls. WhenV the magnetic eld is established at different values, the permeability of the ferromagnetic material is changed and results in altered values of the propagation constant of the waveguide and thereby the phase of microwave energy as it is propagated therethrough.

Other objects and advantages will be apparentfrom the following description and claims considered together with the accompanying drawing in which:

FIG. l is a perspective view of the waveguide structure of a partially assembled two-dimensional antenna array of the present invention;

FIG. 2 is a perspective View of a phaseshifter as employed in the array of FIG. 1;

small physical size, temperature compensation, and high i power handling capabilities.

Itis, therefore, an object to provide a new and improved electronic beam forming and steering antenna system.

Another Objectis to vprovide a xed frequency antenna system for volumetric scanning having a minimum Vnumber of control circuits for the phase- Shifters.

A further object is to provide an antenna system requiring a minimum number of control circuits equal to two. times the number of radiating elements in one d1'- `mension of the antenna array.

A further object is to provide anew and improved yphase shifter having characteristics'that meet the requirementsV for inclusion in an electronic beam forming and scanning antenna system.

A still further object is to provide a phase shifter having a ferromagnetic dieletcric material extended between reduced broad walls of a rectangular waveguide with a static magnetic field through the material parallel to the axis'of the waveguide.

In brief, 'the electronically scanned antenna system of 'the present invention comprises a plurality of radiating muthal angle of the beam from such antenna array is controlled by the relative phase of the Vmicrowave energy between the vertical rows. In a similar manner Vthe elevationaliangle of the beam is Vcontrolled by the relative phase of the microwave energy between the horizontal Thus, Vfor an antenna array of n by m elements, where Vn and m are equal and arranged with the same number of vertical Aand horizontal rows, a raster type Vscan is obtainedwith a minimum number of n-l-mcontrol circuits forthe phase shifting elements.

Asfs'tated previously, the reciprocal phase shifters are the-sameand comprise, Vin general, a section of rectangu- FIG. 3 is a schematic and perspective view, partly in section, of the phase shifter of FIG. 2;

FIG. 4 is Van enlarged cross-sectional view of the phase shifter of FIG. 2, as taken along the line 4-4 of FIG. 3;

FIG. 5 is a perspective view of an assembled antenna array ofthe present invention; and

FIG. 6 is a schematic View of the antenna array of FIG. 5 together with the necessary schematically shown control circuits.

Referring to FIG. l of the drawing, there 'is illustrated the rectangular Vwaveguidestructure of a two-dimensional V antenna array 11 having a plurality of radiating elements 12, which in the present example comprise open ended ,"s'ections of rectangular waveguides 13. As shown, the

array 11 has 64 radiating elements 12, which are suitably 'mounted' inV an 8 by '8 matrix within a first supporting l frame 14.

For a substantially small total angle of scan, about 40 degrees by` 6'0 degrees Without second order beams, the spacebetween radiating elements i the matrix is established at one yinch in both the horizontal and vertical directions. Vertically disposed spacers 16 mounted between elements of the frame 14f provide a radio frequency choke and also the necessary horizontal spacing between "the radiating elements 12 Vwhile the vertical'spacing is pro- VmatrixV of `64 radiating elements, it is to be noted that VAsuch number is merely an example and provides a beam having a 12 degree spread, whereas by increasing the number of radiating elements the beam spread is decreased to -a more desirable pencil shape for radar applications.

The open ended rectangular waveguides'13` thus provide the radiating elements 12 'and are coupled to a similar plurality of rectangular waveguides 17, each having a reciprocal phase shifting element as will be set forth more fully hereinafter. The extended ends of the waveguides 17 are coupled by short coupling rectangular waveguides 18 to paralleland horizontally disposed rectangular feeder waveguides 19, one for each horizontal row of the matrix. Such feeder waveguides 19 are disposed perpendicular to the waveguides 13 with the broad walls also respectively perpendicular and electromagnetic couplingtherebetween is accomplished through conventional slanted -nar- Vrow wall `slots (not shown) in the waveguides I19.

A second supporting frame 21, similar to the first frame 14, is mounted about the coupling waveguides 18 to aid in maintaining the fixed relationship between the radiating elements 12 and both frames may be suitably secured to a stationary platform. The feeder waveguides 19 are extended by separate rectangular waveguide sections 23, each having a phase shifting element similar to those to be described with respect to waveguides 17. To supply microwave energy to the waveguide system just described, a single rectangular waveguide 24 is provided for suitable coupling to a source of microwave energy (not shown) and extended perpendicular to the waveguide sections 23 with the broad walls respectively perpendicular and with electromagnetic coupling again accomplished by conventional narrow wall slots (not shown) and substantially in the single waveguide 24 and short-length rectangular waveguide sections 25.

Referring now to the waveguides 17 and 23, in detail, there is shown in FIG. 2 -a perspective view of a typical waveguide (indicated generally by numeral 26 for reference purposes) having `a reciprocal phase shifting element. Coupling flanges 27 are provided at either end along the transverse dimension of the broad walls of rectangular waveguide 26 for suitable connection to other waveguides, in accordance with the foregoing. By omitting similar coupling flanges along the narrow walls of the waveguides 26, a plurality of such waveguides may be suitably bound together with portions of the narrow walls of adjacent waveguides touching and the desired distance between radiating elements 12 obtained.

Adjacent to each end of the waveguide 26 there is provided a tapered portion 27a to reduce the broad wall dimension by a predetermined amount such, for example, as from .9 to substantially .6 for conventional RG-52 waveguide. A straight center portion 28 at the reduced broad wall dimension then extends between the tapered portions 27a. It is to be noted that the tapered portions 27a provide minimum impedance mismatch for microwave energy propagated therethrough in that there are no abrupt discontinuities in the walls of the waveguide. Thus, when waveguides 26 `are stacked with narrow walls of adjacent wavegu-ides facing each other, there is a space between the two walls for accommodating the turns of solenoids 29 as ywound about the center portions 28.

As stated previously each of the waveguides 26 is provided with a phase shifting element, which, as illustrated in FIG. 3, comprises an elongated substantially thin slab 31 of a ferromagnetic dielectric material, such as ferrite, having a permeability that is variable with variation of an applied magnetic field. The ferrite slab 31 is mounted centrally within the center portion 28 of the waveguide 26 parallel to the narrow walls and transverse to the reduced broad walls, as best shown in FIG. 4. To minimize voltage reflections from the ferrite slab 31 both ends thereof are tapered to a point or wedge which extend from the center portion 28 into the respective tapered portions 27a. It is to be noted that the reduced broad wall dimension of .6" is beyond the cutoff of the waveguide 26 at X-band frequencies; however, it has been found that energy propagation is normal 4when the ferrite slab 31 is mounted in the waveguide in the above specified manner.

In accordance with the invention, it is necessary that changes in phase shift be accomplished with high speed at small average values of magnetic field establishing current. One step toward realization of such characteristics is embodied in the reduction of the broad wall dimension of the waveguide 26 at the center portion 28. Though this referenced reduction -was necessary to achieve sufficient space between stacked waveguides 26 for the j placement of the windings of solenoids 29, it also provides a minimized length of path for a magnetic field established by the solenoid longitudinally through the ferrite slab 31. This means that a given value of magnetization of the ferrite slab 31 is accomplished by a lesser number of solenoid ampere-turns than is possible with a longer 4 path; that is, the smaller the diameter of the solenoid, the more concentrated the axial portion of the magnetic eld for a given value of excitation current.

A second step toward obtaining fast switching of phase with such structure is accomplished by minimizing the shorted-turn effect of the walls of the waveguide 26. This accomplishment is embodied in the utilization of substantially thin conductive walls, which may be a ceramic type of waveguide with the inside surfaces having a thin coating of conductive material. Preferably, however, for reasons to be set forth hereinafter, the waveguide 26 is shaped from a rectangular section of RG-SZ waveguide by milling off the sides or narrow walls and then reducing the dimensions of the broad walls to those previously specified. The resulting open sides are then covered with an insulating material 32, such as plastic, having a thin conductive layer 33, such as one mil brass or copper foil. The foil 33 is then conductively connected to the remaining walls of the waveguide 26, as by sweat soldering. Thus, when current flows through the solenoid 29 there is a minimum of eddy current losses and the one mil foil is suicient to prevent radio frequency leakage losses.

Having reduced the physical size of the phase shifter waveguide 26 over previously known devices of this type and provided fast switching with low values of magnetic eld establishing current, another required characteristic relates to temperature compensation. With respect to this characteristic, it is to be noted that when a ferrite material is magnetized in the presence of microwave energy, heat is developed in the ferrite and this results in a change of permeability. Since the propagation constant is a function of permeability, changes in temperature alter the propagation constant and thereby change the degree of phase shift of propagated energy with other variables held constant. To minimize temperature effects the ferrite slab 31 is mounted in the waveguide 26 in thermal contact with the broad walls which are of conventional thickness and thereby provide a suitable heat sink. To improve the phase shift eciency a thin layer 34 of thermal conducting ceramic, such as boron nitride or barium oxide, is disposed between the ferrite slab 31 and the broadwalls of the waveguide 26 and thermal conductivity is thereby maintained.

With the phase shifter waveguide 26 assembled in the foregoing manner with leads 36 and 37 of the solenoid suitably connected to a source of current, a ow of current through the solenoid establishes a magnetic field axially within the waveguide and through the ferrite slab 31. This magnetic field establishes the permeability of the ferrite material of the slab 31 at a certain value and therefore sets the propagation constant of the waveguide so that microwave energy as propagated through has a difference in phase between the respective ends. Because the slab 31 is centered in the waveguide 26 along the plane of maximum electric field, ener-gy in the dominant mode which is propagated in either direction is similarly shifted in phase. With the solenoid 29 having about turns the phase shifter waveguide 26, `as previously described, provides a zero to 360 degree phase shifting time on the order of one microsecond, which is a great improvement over the minimum .5 second switching time obtainable with prior art devices. Also minimum temperature effects with respect to the ferrite slab are achieved by the thermally conductive contact between the slab and the broad walls of the waveguide 26.

Having described the phase shifting waveguides 17 and 23 in detail the nal assembly of the antenna will now be set forth with reference to the perspective view of FIG. 5. Each of the waveguides 17 and 23 of FIG. 1 is provided with a solenoid 29 and to prevent interaction of the magnetic fields of adjacent solenoids, magnetic shielding is provided such as a thin layer 38 (see FIG. 4) of magnetic iron sheeting suitably secured xabout the windings of each of the solenoids. To prevent free circulation of air about the assembled phase shifting waveguides 17 and 23 and to provide mounting of ielectrical terminals 39 and 441 for connection of azimuth and elevation scan control circuits, respectively, panels 41 of an electrical insulation material, such `as phenolic, arel suitably mounted to respectively cover .the open sides of such waveguide assemblies.

For some installations where the surrounding temperature is substantially constant as in some land-based installations, the heat sink effect provided by the brass walls of the waveguides is sutlicient to maintain ka substantially constant temperature for 'the ferrite elements after a relatively short warm-up period of operation. In other installations it may be necessary to provide heater elements within the enclosure formed by the panels 41 with conventional thermostatic control elements coupled to the heaters. In both such instances temperature-change eects are minimized withrespect to the yphase shifting ferrite elements 31 so that a given value of magnetization of the ferrites provides in eachrinstance substantially the same degree of phase shift of the propagated microwave energy. Additionally, in some installations, it may be necessary -to provide a dielectric material to cover the open ends of the radiating elements 12 to prevent a iiow of external air `from reaching the ferrite elements 31 through such openings.

To control the azimuth scan of the beam :from the assembled array 11 one lead 36 of each of the solenoids 29 of one vertical row of phase Shifters is connected to one of the terminals 39. The referenced terminal39 is connected to a movable contact 47 of a conventional stepping switch 48 having in the present example 8 fixed contacts 51458. A precision resistor 59 is connected between the output terminals of the source 46 and separate -taps of such resistor are respectively connected to the fixed contacts 51-58 to provide a diierent value of voltage for each contact. A similar stepping switch 48 and current control circuit is provided for each of the remaining vertical rows of solenoids 29 .and because of the similarity only one such switch and circuit has been illustrated in FIG. 6 and described in detail. One difference with respect to the stepping switches 48 is to be noted and this relates to the relative positions between the movable and xed contacts respectively, which is established so that successive switches rapply incrementally increased values of current.

With respect to the elevation scancontrol circuits one lead 36 of one solenoid 29 of the vertical phase Shifters is connected to a movable contact 62 of another conventional stepping switch 63 having 8 fixed contacts 64 to 71. Again arprecision resistor 76 is connected between the output terminals of the current source 61 with taps respectively connected to the fixed contacts 64 to 71 to provide incremental values of current to the solenoid 29. Additional stepping switches 63 and associated control circuit` connections are the same for the remaining solenoids of the phase shifter 23 and only one is detailed in FIG. 6 for clarity of illustration. As with the phase Shifters 17, phase shifters23 are provided with successively increased increments of current for any one position of the stepping switches 63.

Thus, by separately and simultaneously operating the stepping switches'48 and 63, a beam radiated by the 64 elements of the antenna array 11 may be readily controlled in azimuth and elevation by the establishment of` phase differences between the microwave energy fed to respective vertical rows of radiating elements and of phase differences between the horizontal rows of radiat- -ing elements. With the improved methods of manufacturing ferrite materials the selection and forming-to-size of those elements operated in parallel relation to provide substantially equal phase shifts `for a given value 4of magnetic field is relatively simple. Itis ValsoV to be noted that should hysteresis eects occur in `the`ferrite elements of the phase shifter'l and 23 during 4the switching "6 period, such effects may be readily minimized by applying a current to solenoids 29 resulting in a saturating field through the elements during this period, as conventionally indicated by switches 79, which may be mechanically linked to the associated stepping switch 48, 63.

While the scanning control circuits have been set forth in detail with respect to the combination of precision resistors 59, 76, yandV stepping switches 48, 63, it is to be noted that suitably timed conventional electronic circuitry,'either vacuum tube or transistor, may be readily provided with the timing programmed by a simple computer. This latter consideration is to be particularly considered where -a faster rate of scan is desired than the approximate 30 scans per minute, which is permissible with the stepping switches 48 and 63, as described, and which are limited to a switching time of about 32 per second.

In the presently described embodiment ofthe invention the radiating elements 12 are inductive matched irises formed by the open ends'of waveguides 13 with inductive side plates 81 mounted between the broad walls to extend interiorly and perpendicularly from the narrow walls. While the inductive matched iris type of radiating element 12 is suitablefor a total scan angle of about 40V degrees, other types may be desirable for larger scan angles and these are within the knowledge of the `art.

`Consider now the operation of `the antennasystem, as described in detail in the. foregoing, with reference being made to the drawing and particularly to FIG. 6. Microwave energy is introduced to theV input of waveguide'24 and propagated therethrough in the dominant mode. A portion of the energy is electromagnetically coupled from waveguide 24 into each of the phase Shifters 23 in the conventional manner. VThe stepping switches 63 associated with the respective solenoids 29 of the phase Shifters 23 respectively establish incrementally different values of current through the solenoids and this results in incrementally dierent values of magnetic'iield through the phase shifting ferrite slabs 31. Thus, with suitable settings of the initial and subsequent positions between the movable 'and iixed contacts of the stepping switches 63, the permeability of the slabs 31 is established to provide relative phase shifts between zero and 360 degrees in successive 45 degree steps for the example shown. Thus, the microwave energy propagated by the eight feeder waveguides 19 diiers in phase by 45 degrees between adjacent waveguides and, since each of the waveguides feeds a single horizontal row of eight radiating elements 12, the relative phase of the energyof the adjacent rows determines the elevational angle of the resulting beam.

The phase Shifters 17 coupled between feeder waveguides 19 and the individual radiating elements 12 are similarly controlled; however, the phase shifters of each vertical row are controlled to provide a similar shift in the phase of the microwave energy for each such row. Thus, by suitable settings of the initial'and subsequent positions between the moveable and iixed contacts of the stepping switches 48, the relative phase of the microwave energy of vertical rows of radiating elements 12 is established. The azimuthal direction of the beam may then be readily established by proper control ofthe operation of the stepping switches 48.

In the foregoing it has been shown that the Vdirection of the beam is controlled in azimuth by the stepping switches 48 and in elevation by the stepping switches 63. When the two sets of stepping switches 48 and 63 are simultaneously operated from a position where the relative phase of one radiating element 12 is zero, a raster type beam scan of space is readily obtained. This latter operative relationship is shown in FIG. 6k where the phase Shifters 23 are indicated as introducing phase shifts varying by incremental angles from Zero to 8 'fp from topto bottom and the phase shifters 17 are indicated as introducing by vertical rows Simi-lar phase shifts varying by incremental angles from zero to 8 0 from left to right. With the phase Shifters 23 of the feeder waveguides maintained in the same condition, operation of the Stepping switches 48 to shift the relative phases of the vertical rows to the right results in azimuth translation of the beam. When the relative phases of the radiating elements 12 are in reversed order from the initial relationship set forth above, the stepping switches 63 are operated to alter the phase condition of the feeder waveguides 19 so that the zero-Zero phase shift relation between the two Sets of phase Shifters 17 and 23 coincides at the left column, second row down. By continuing the foregoing operation procedure, an 8 by 8 raster is scanned and, since the phase Shifters 17 and 23 are reciprocal, return echos are received for application to a receiver as is usual in conventional radar equipment.

There has been set forth in the foregoing a reciprocal phase Shifter having accurate high Speed switching, economy of driving power, and small physical size for an allphase shifter type of volumetric scanning antenna system requiring a minimum number of control circuits. This antenna System is capable of raster-type scan of space covering 90 degrees by 90 degrees with a pencil type beam.

While the salient features of the invention have been described in detail with respect to one embodiment, it will be readily apparent that numerous modifications may be made within the spirit and scope of Ithe invention and it is, therefore, not desired to limit the invention to the exact ldetails shown except insofar as they may be set forth in the following claims.

What is claimed is:

1. In a system for volumetric scanning with a radiated beam, the combination comprising a plurality of radiating elements geometrically spaced in a two-dimensional array with n rows along one dimension and m columns along the other dimension, waveguide means for coupling said radiating elements to a Source of fixed-frequency microwave energy, said waveguide means including a first phase shifting means for varying the phase of said energy between adjacent n rows, said waveguide means including second phase Shifting means for varying the phase of said energy between adjacent m rows.

2. In a system for volumetric scanning with a radiated beam, the combination comprising a plurality of radiating elements geometrically spaced in a two-dimensional array with n rows along one dimension and m rows along the other dimension, a Similar plurality of variable phase Shifters respectively coupled tto said radiating elements and having separate control elements, a source of high frequency energy, separate variable phase shifting means coupled between phase Shifters of each m row of radiating elements and Said source with each such means having separate control elements, first control means coupled to the control elements of said phase Shifters disposed along n rows for establishing a predetermined phase shift of energy for each n row and phase difference between adjacent n rows, and second control means coupled :to the control elements of said phase shifting means for establishing a predetermined phase shift of energy for each m row and phase difference between adjacent m rows, whereby subsequent separate adjustments of said first and second control means provides beam scanning by m plus n control means.

3. In a system for volumetric scanning with a radiated beam, the combination comprising a plurality of radiating elements geometrically spaced in a two-dimensional array with n rows along one dimension and m rows along the other dimension, a lfirst plurality of variable phase Shifters respectively coupled to said radiating elements, a source of fixed-frequency microwave energy, a second plurality of variable phase Shifters respectively coupled between phase Shifters in m rows of said rst plurality and said 8 source, each of said rst and second plurality of phase Shifters having elements of a ferromagnetic dielectric materialwith variable permeability, first control means coupled to said first plurality of phase Shifters for varying the permeability of the elements by rows with the variation in each row being to the Same degree to establish different values of permeability between adjacent n rows, and second control means coupled to the second plurality of phase shifters for individually varying the permeability of the elements thereof to establish different values of permeability between adjacent m rows, whereby subsequent separate adjustments of said first and second control means provides Ibeam scanning by m plus n control means.

4. In a System `for volumetric scanning with a radiated beam, the combination comprising a plurality of rectangular waveguides mounted in parallel relation to provide at ends thereof a plurality of radiating elements geometrically spaced in a two-dimensional array with n rows along one dimension and m rows lalong the other dimension, rectangular waveguide means coupled between said plurality of waveguides by m rows to a source of fixed-frequency microwave energy, said waveguide means including means for varying the phase of said energy between adjacent n rows and separate means for varying the phase of said energy between adjacent m rows, and a programmer coupled to said means for varying the relative phases to provide a raster-type beam scanning pattern.

5. In a system for volumetric scanning with a radiated beam, the combination comprising a plurality of radiating elements geometrically spaced in a two-dimensional array with n rows along one dimension and m rows along the other dimension, waveguide means for coupling said radiating elements by m rows to a source of Xed-frequency microwave energy, Said waveguide means including first ferrite phase Shifters with one for each radiating element and separate second ferrite phase Shifters between said rst phase Shifters and said source with one for each m row, separate solenoids wound on said waveguide means for each of said first and second phase Shifters, means for selectively connecting said solenoids o-f said first phase Shifters by n rows to different current sources, means for selectively coupling solenoids of said second phase Shifters to different current Sources, and means for programming relative values of current of said current sources to provide a raster type scan with a radiated beam of said microwave energy.

6. In a system for volumetric scanning with a radiated beam, the combination comprising a plurality of rectangular waveguides mounted in parallel relation to provide at ends thereof a plurality of radiating elements geometrically spaced in a two-dimensional array with n rows along one dimension and m rows along the other dimension; a first plurality of phase Shifters; a Source of fixed-frequency microwave energy; a second plurality of phase Shifters coupled between phase Shifters of said rst plurality by m rows and said source of microwave energy; each of said first and second plurality of phase Shifters comprising a section of rectangular waveguide having a portion with reduced broad wall Width accommodating a solenoid Wound thereabout and with a ferrite slab mounted centrally within Such portion perpendicular to and in thermal contact with the reduced broad walls, and a magnetic shield disposed about said solenoid; means for selectively connecting said solenoids of said rst plurality of phase Shifters by n rows to different current sources; means for selectively coupling solenoids of said second plurality of phase Shifters to different current sources; and means for programming relative values of current of said current sources to provide a raster type scan with a radiated beam of said microwave energy.

7. In a system for volumetric scanning with a radiated beam, the combination comprising a plurality of rectangular waveguides mounted in parallel relation to provide at ends thereof a plurality of radiating elements geo- 9 metrically spaced in a two-dimensional array with n rows along one dimension and m' rows along the other dimension; a rst plurality of phase Shifters; a source of xed-frequency microwave energy; -a second 1i) for selectively coupling solenoids of said second plurality of phase shifters to diiferent current sources; and means for programming relative values of current of said current sources to provide a raster type scan with a raplurality of phase Shifters coupled between phase Shifters 5 diated beam of said microwave energy.

of said rst plurality by m rows and said source of microwave energy; each of said rst and second plurality of phase Shifters being reciprocal and comprising a section of rectangular waveguide having a portion with reduced broad wall width, tapered transition portions extended at either end of said reduced portion, nonconductive narrow walls with thin conductive layers on interior surfaces, a ferrite slab mounted centrally within such portion perpendicular to and in thermal contact with the reduced broad walls, a solenoid wound about the reduced portion and -accommodated thereby, and a magnetic shield disposed about said solenoid; means for selectively connecting said solenoids of said irst plurality of phase Shifters by n rows to different current sources; means References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES IRE Proceedings, vol. 45, No. 1957, pp. 1510-1517. 

